Shell实践

1
2
3
4
5
6
7
8

# 增加.sh后缀为了方便脚本类别识别
touch demo.sh
vim demo.sh
# '#'是注释，不会被shell解释
# '#!' 标记为 当前脚本需要怎样shell解释器执行
#!/bin/bash
# echo 标准输出器后面的内容
echo "Hello shell"

1
2
3
4
5
6

# 给脚本文件增加执行权限
chmod +x demo.sh
# 就在当前目录查找demo.sh并执行
# 除此之外，linux会从PATH中查找待执行脚本并执行
./demo.sh
# sh demo.sh

1
2
3
4

# 格式化 %占位 最好用双引号将格式化模板包裹
# 参数列表使用空格分隔
# 如果参数数量不一致，后面将使用%后面对应默认数值返回
printf "%d %s\n" 10 "abc"

1
2

read arg
echo "Hello ${arg}"

1
2
3
4
5

ARG="shell"  # 声明并赋值 =号两边不要存在空格
echo ${ARG}  # 通过${变量}解释变量名

readonly ARG  # readonly将ARG定义为只读变量，不能被修改
unset ARG     # 解绑变量或者理解删除变量

1
2
3
4
5

# 命令替换
# 反引号包裹shell命令集合，会将这个执行结果存储于临时变量
DATE=`date`
echo ${DATE}
# Sun Jun 26 21:12:04 CST 2022

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

DATE=`date`
echo ${DATE:+'arg'}
# arg
echo ${DATE}
# Sun Jun 26 21:25:03 CST 2022
unset DATE
echo ${DATE:?NONE}
# -bash: DATE: NONE
echo ${DATE:-arg}
# arg
echo ${DATE:=$(date)}
# Sun Jun 26 21:29:33 CST 2022
echo ${DATE}
# Sun Jun 26 21:29:33 CST 2022

1
2
3
4
5
6

# arg=`2 + 2` --> bash不支持
# expr 2+2 --> 2+2
expr 2 + 2
# 4
arg=`expr 2 \* 2`
echo ${arg}

1
2
3
4
5
6
7
8

#!/bin/bash
a=10;b=20
# [[ ${a} -ne ${b} ]]; 注意空格
if [[ ${a} -ne ${b} ]]; then
    echo "${a} not qual to ${b}"
else
    echo "${a} qual to ${b}"
fi

1
2
3
4
5
6
7
8

# 字符串长处
str='Bash Shell Script'
echo ${#str}
# 字符串切片
echo ${str:1}  # ash Shell Script
echo ${str:1:4}  # ash
echo ${str:0}  #  Bash Shell Script
echo ${str:-1}  #  Bash Shell Script

 1
 2
 3
 4
 5
 6
 7
 8
 9
10

array=(1, 2, 3, "shell")
echo ${arry}
echo ${array[2]} #读取下标为2的元素
echo ${array[*]} #读取所有元素
echo ${array[@]} #读取所有元素


echo ${#arrae[*]} #获取数组长度
echo ${#arrae[@]} #获取数组长度
echo ${#arrae[1]} #获取数组中单个元素的长度

 1
 2
 3
 4
 5
 6
 7
 8
 9
10

#!/bin/bash
a=10;b=20
# [[ ${a} -ne ${b} ]]; 注意空格
if [[ ${a} -gt ${b} ]]; then
    echo "${a} great to ${b}"
elif [[ ${a} -lt ${b} ]]; then
    echo "${a} less to ${b}"
else
    echo "${a} equal to ${b}"
fi

 1
 2
 3
 4
 5
 6
 7
 8
 9
10

#!/bin/bash
grade="B"

case ${grade} in   # in 不能少
    "A") echo "great";;  # case的匹配方式 ;; 结束匹配
    "B") echo "good";;
    "C") echo "gerular";;
    *) echo "Sorry"; echo "fighting";; # 其余或者理解为default
    # ?) echo "Sorry"; echo "fighting";; # 其余或者理解为default
esac

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22

#!/bin/bash

# 遍历字符串
for ch in 'This a test'; do
    echo ${ch}
done

# 遍历数组
for num in 1 2 3 4; do
    echo ${num}
done

# 遍历当前目录
for f in *; do
    echo ${f}
done

# 遍历文件内容
fc=`cat test.log`
for fc_q in ${fc}; do
    echo ${fc_q}
done

1
2
3
4
5
6
7

#!/bin/bash

c=0;
while [[ ${c} -lt 3 ]]; do
    echo "Curr Val is ${c}"
    c=`expr ${c} + 1`
done

1
2
3
4
5
6
7

#!/bin/bash

c=0;
until [[ ${c} -eq 3 ]]; do
    echo "Curr Val is ${c}"
    c=`expr ${c} + 1`
done

 1
 2
 3
 4
 5
 6
 7
 8
 9
10

#!/bin/bash

# 定义函数
function hello() {
    echo "Hello Shell"; ## 如果是指出return 最后一句将作为返回值返回
    return ; ## 返回值只能是整数，0标识成功，其他至标识失败
}

# 调用函数,不用加()
hello

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19

#!/bin/bash

## 获取参数是在函数内部获取，在调用函数传入
function sum() {
    case $# in  ## 获取入参格式
        0) echo "No param";;
        1) echo $1;;
        2) echo `expr $1 + $2`;;
        *) echo "$# params！It's too much!";;
    esac
}

sum 1;
sum 1 2;
sum 1 2 3;

# 获取函数返回值
s=$(sum 1 2)
echo "func resturn ${s}"

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18

#!/usr/bin/bash

# 输出重定向
touch test.log
which bash > test.log
who > test.log  # 覆盖which bash数据作为新的数据内容
which bash >> test.log  # 追加至原有数据的后面

# 输入重定向
# cat test.log <--> cat < test.log 等价
wc -l < test.log

# command 2 > file  将stderr重定向至file
# command 2 >> file  将stderr追加至file
# command > file 2>&1  stdout 和 stderr 合并后重定向到 fil
# command < file >file2 stdin 和 stdout 都重定向

# /dev/null 最为垃圾站的使用